1. Field
This patent specification describes a method and apparatus for image forming, and more particularly to a method and apparatus for image forming using an ink-jet printing system capable of easily replacing an ink carriage including an ink-jet print head.
2. Discussion of the background
Ink-jet printing systems are commonly used in various image forming apparatuses such as printing machines, facsimile machines, copying machines, MFP (multifunction peripheral) machines and the like. Generally, a background ink-jet printing system includes an ink carriage and an ink-jet print head. The ink-jet print head includes a plurality of nozzles formed on a surface thereof and is mounted on the ink carriage. The ink-jet print head is mounted on the ink carriage. When a recording medium is conveyed to a printing area of the ink-jet printing system, a surface of the ink-jet print head faces a surface of the recording medium. At this time, a predetermined gap is provided between the ink-jet print head and the recording medium. When the background ink-jet printing system performs an image forming operation, the ink carriage slidably travels from side to side of the recording medium. At this time, the ink-jet print head sprays ink drops through the plurality of nozzles directly onto the surface of the recording medium.
The background ink-jet printing system generally employs one of two structures for supplying ink. In one structure, the ink carriage integrally mounting the ink-jet print head and an ink container thereon reciprocally moves from side to side of the recording medium. In the other structure, the ink-jet print head is mounted on the ink carriage and the ink container is fixedly provided to the background ink-jet printing system, and ink is supplied through a tube arranged to connect the ink-jet print head and the ink container.
The ink-jet print head provided to the background ink-jet printing system may be detachably removable with respect to the ink carriage. The ink-jet print head as described above can easily be replaced by an end user, and at a same time, an accurate positioning is required for the plurality of nozzles formed on the ink-jet print head. Further, the background ink-jet printing system may include an ink-jet print head unit which integrally supports a plurality of ink-jet print heads. The ink-jet print head unit is detachably mounted on the ink carriage and is required to accurately be positioned in the event of the replacement thereof. To increase the above-described positioning accuracy, improved structures of the ink-jet print head and the ink carriage have been proposed.
In addition, the ink carriage with the ink-jet print head mounted thereon is slidably supported by a guiding shaft provided to the background ink-jet printing system such that the ink carriage can reciprocally move along the guiding shaft. When the ink carriage is provided in an ink cartridge, the ink carriage reciprocally moves along a longitudinal direction of the ink cartridge.
Referring to FIG. 1, a structure of a background ink-jet printing system 1 is explained. The background ink-jet printing system 1 of FIG. 1 is viewed from a surface side of a recording medium in a printing area. The background ink-jet printing system 1 includes an ink carriage 2, a guiding shaft 3, a plurality of ink-jet print heads 4a, 4b, 4c and 4d, and a plurality of nozzles having end nozzles 5a, 5b, 5c and 5d. The ink carriage 2 reciprocally moves along the guiding shaft 3 in a direction as indicated by an arrow shown in FIG. 1. The plurality of ink-jet print heads 4a, 4b, 4c and 4d are integrally mounted on the ink carriage 2. The plurality of ink-jet print heads 4a, 4b, 4c and 4d include the plurality of nozzles having end nozzles 5a, 5b, 5c and 5d, respectively, on each predetermined side thereof. It is desirable the end nozzles 5a, 5b, 5c and Sd are positioned at equal distances from a shaft line 3a which is a line extending in a longitudinal direction of the guiding shaft 3. In FIG. 1, the end nozzles 5a, 5b, 5c and 5d are variably positioned on the ink-jet print heads 4a, 4b, 4c and 4d, respectively. The end nozzles 5a and 5d are disposed at positions equally away from the shaft line 3a and their distance from the shaft line 3a is shortest among the end nozzles 5a, 5b, 5c and 5d. The distance between each of the end nozzles 5a and 5d and the shaft line 3a is defined as a distance Y1. The end nozzle 5b is disposed at a position furthest away from the shaft line 3a and a distance between the end nozzle 5b and the shaft line 3a is defined as a distance Y2. The end nozzle 5c is disposed at a position between the distances Y1 and Y2. A difference between the distances Y1 and Y2 is defined as a distance Y3. When an amount of the distance Y3 is closer to zero, the end nozzles 5a, 5b, 5c and 5d are determined to be desirably positioned. Further, it is desirable angles θ1, θ2, θ3 and θ4 of respective nozzle lines 6a, 6b, 6c and 6d are right angle with respect to the shaft line 3a. Additionally, a distance between the nozzle lines 6a and 6b is defined as a distance X1, a distance between the nozzle lines 6b and 6c is defined as a distance X2, and a distance between the nozzle lines 6c and 6d is defined as a distance X3. It is desirable the distances X1, X2 and X3 are set to a predetermined value. As described above, when positions between the ink carriage 2 and each of the plurality of ink-jet print heads 4a, 4b, 4c and 4d are adjusted, positions between the guiding shaft 3 and each of the end nozzles 5a, 5b, 5c and 5d need to be fixedly adjusted and positioned. The adjustments as described above can increase an accuracy of replacement of the ink carriage 2 and obtain a high quality image.
However, the background ink-jet printing system 1 of FIG. 1 employs a structure in which the plurality of ink-jet print heads 4a, 4b, 4c and 4d are detachably removable with respect to the ink carriage 2. This structure requires high component reliabilities of the ink carriage 2 and the plurality of ink-jet print heads 4a, 4b, 4c and 4d for positioning, and high positioning accuracies of the plurality of ink-jet print heads 4a, 4b, 4c and 4d with respect to the plurality of respective nozzles having the end nozzles 5a, 5b, 5c and 5d. These requirements of the high positioning decrease a positioning accuracy of the plurality of nozzles having the end nozzles 5a, 5b, 5c and 5d with respect to the guiding shaft 3. Therefore, a high quality image can hardly be obtained.
Referring to FIG. 2, another case of replacing the components of the background ink-jet printing system 1 is explained. As previously described, the ink carriage 2 is slidably supported by the guiding shaft 3 of the background ink-jet printing system 1. Two side plates 7 and 8 are provided at both ends of the guiding shaft 3 for supporting the guiding shaft 3 holding it through holes formed on respective surfaces of the side plates 7 and 8. An ink-jet print head cleaning mechanism 9 is provided to a position under the ink carriage 2 for cleaning the ink-jet print heads 4a, 4b, 4c and 4d of FIG. 1. A cap (not shown) may also be provided to a position under the ink carriage 2 for keeping the ink-jet print heads 4a, 4b, 4c and 4d moist.
When detaching an entire unit of the ink carriage 2 with the plurality of the ink-jet print heads 4a, 4b, 4c and 4d mounted thereon from the ink-jet printing system 1, an operator performing the replacement firstly removes retaining rings (not shown) from both ends of the guiding shaft 3 and then pulls out the guiding shaft 3, in a direction indicated by an arrow, from the holes on the side plates 7 and 8 and the ink carriage 2. At this time, the operator needs to hold the ink carriage 2 to prevent it from falling when the guiding shaft 3 no longer supports the ink cartridge 2. In a case where the ink carriage 2 falls, the fall may cause damages on a surface of the ink-jet print heads 4a, 4b, 4c and 4d, and damages to the cap and the ink-jet print head cleaning mechanism 9. Further, the operator needs to hold a new ink-jet carriage when attaching it to the ink-jet printing system 1. This may cause the damages as described above and reduce an operability of the replacement.